Summary
Unit and Measurements
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Systems of units are made up of a small number of base units, which
are known by accurate and precise measurements of conventionally
chosen base quantities. Other units are then derived as algebraic
combinations of the base units.
Two known systems of units usually used are English units and SI units.
Scientists and most of the other people in the world use SI.
SI base units of length, mass, and time are the meter (m), kilogram (kg),
and second (s), respectively.
SI units are a metric system of units, meaning values can be calculated
by factors of 10. Metric prefixes may be used with metric units to scale
the base units to sizes appropriate for almost any application.
Conversion
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Upon conversion of a quantity from one unit to another, multiply by
conversion factors in such a way that you cancel the units you want to
cancel and introduce the units you want to end up with.
Be careful with areas and volumes. Units should follow the rules of
algebra, for example, if a unit is squared we need two factors to cancel
it.